Domestic Hot Water & Hot Water Return Coupling

[DavZ1500]

Hello,

I am having trouble keeping the System Type's I have defined for domestic hot water and domestic hot water return piping when I try to connect the two together. If you were to try to "tee" the systems together, Revit defaults to changing the system type to one of the two, thus I lose one of the systems. I have managed to create a generic coupling so I can connect the two, however, the fitting will only maintain the "coupling plan symbol" if I keep the same pipe size on both sides. In many situations, the domestic hot water return will be 1/2" and the domestic hot water may be 1". When I change the pipe sizes, Revit changes the pipe accessory from my coupling to a reducer with different symbols. 

Does anyone have any recommendations or solutions they implement to solve these issues? 

The photo below I started at the bottom with 3/4" and here is what is happening when I change pipe sizes.

[iainsavage]

The recommendation is to not physically connect the return into the flow in order to avoid the issue that you are having.

Been there, done that, wasted hours disconnecting and capping the “connections”.

I’m pretty sure that advice is in official autodesk help somewhere.

You will also not be able to do calculations on your hot water flow pipework if you connect the returns.

Note that the hot water flow should be Domestic Hot Water but the return would normally be Hydronic Return (because the return does NOT use fixture units as the flow method).

Hope this helps.

[ceyhunyuzuak]

there is a workaround for this but what kind of scenario is this there you connect DHW to HWR without anything inbetween?

anyway

what you are supposed to do is go into that coupling family;

1. pick connection elements and set both of them to be Global system classification.

2. set flow direction one is "in" other is "out".

3. if you want to keep the flows in a coordination you should set one connector element as preset and the other one calculated based on which side defines the flow rate. for instance let's say your DHW system accumulates the end point needs and has already flow defined at the end. pick the connector element that has flow direction defined as "out" (assuming here your "out" side is DHW) and set its flow configuration "Calculated" and the other one as "Preset". bind both of their "Flow" to the same instance parameter you create. just create one and name it something.

4. go to family category an parameters and select mechanical equipment (yes it has to be a mechanical equipment)

save as the family with a name you decide.

there you go.

[DavZ1500]

As an example, DHW piping will tie directly into the HWR to create a piping loop in the building. Typically this is done with either a "tee" fitting at the end of the DHW before the last fixture, or the DHW essentially becomes the HWR and loops back to the water heater. 

I am not interested in Revit performing any of the calculations, I just need the piping system to display the correct line type on plan. Would you recommend I start with a coupling family to begin with or do I need to start with a new family? Thank you for the help.

[ceyhunyuzuak]

I still didn't get your system, that sounds like to me that it is something like, so called, "circulation line" that is used to circulate DHW in the whole building just in order to keep hot water reachable within seconds when user opens a tap.

you can pick or make anything that has at least 2 pipe connectors on and use it. by the way, don't link the connectors. if there is a link, break it please.

[iainsavage]

The flow rate in a domestic hot water return is NOT the same or in any way related to the flow rate in the flow/supply pipe. It is NOT related to the fixture unit method for determining flow rates from plumbing fixtures.

The flow rate in the domestic hot water return only serves the function of keeping the system warm and it is calculated by estimating the rate of heatloss from the whole distribution system pipes, allowing a defined temperature difference between the flow out of the cylinder and the return into the cylinder and using the formula Q=mC(dT) to convert the pipe heatloss to a water flow rate (Q is heat loss, m is mass flow of water, C is specific heat capacity of water, dT is temperature difference between flow out and return in at cylinder). The flow in each return branch is worked out by apportionment of the overall total.

Therefore the method that you have outlined for passing the flow rate from the flow to the return is NOT correct.

If you want to use calculations on the Domestic Hot flow pipe do NOT make a return connection (in Revit, obviously you would in real world).

If you want to use calculations on the domestic hot water return pipe, make it Hydronic Return classification, make a customised cap fitting which has a Hydronic Return out connector, preset, and associated to an instance flow parameter. You would then need to manually populate the flow value (calculated from the apportionment of the system heatloss) for each cap (at least I’m pretty sure Revit won’t do this automatically).

In my opinion.

[iainsavage]

If you’re not interested in calculations then in theory you can connect different systems together but you have to use a particular method.

There must be an isolating fitting between the two systems. 
An elbow or tee should work.

What you have to do is draw a pipe out of the flow pipe to generate the branch.

Then delete the branch pipe.

Then draw your return pipe TOWARDS the branch connection. Do NOT draw away from the branch connection.

The different systems should then be retained.

If you search for how to connect vent pipe to waste pipe you’ll find information on the method including videos - same principle.

[ceyhunyuzuak]

---

@iainsavage wrote:

The flow rate in a domestic hot water return is NOT the same or in any way related to the flow rate in the flow/supply pipe. It is NOT related to the fixture unit method for determining flow rates from plumbing fixtures.

The flow rate in the domestic hot water return only serves the function of keeping the system warm and it is calculated by estimating the rate of heatloss from the whole distribution system pipes, allowing a defined temperature difference between the flow out of the cylinder and the return into the cylinder and using the formula Q=mC(dT) to convert the pipe heatloss to a water flow rate (Q is heat loss, m is mass flow of water, C is specific heat capacity of water, dT is temperature difference between flow out and return in at cylinder). The flow in each return branch is worked out by apportionment of the overall total.

Therefore the method that you have outlined for passing the flow rate from the flow to the return is NOT correct.

If you want to use calculations on the Domestic Hot flow pipe do NOT make a return connection (in Revit, obviously you would in real world).

If you want to use calculations on the domestic hot water return pipe, make it Hydronic Return classification, make a customised cap fitting which has a Hydronic Return out connector, preset, and associated to an instance flow parameter. You would then need to manually populate the flow value (calculated from the apportionment of the system heatloss) for each cap (at least I’m pretty sure Revit won’t do this automatically).

In my opinion.

---

I believe you were supposed to address this to @DavZ1500 rather than me, is that right?

I believe you didn't dare to teach me utterly basic thermodynamics, heat transfer and fluid mechanics. right, sir?

[RobDraw]

No need to be condescending. Isn't it obvious who he was speaking to? The format of the two reply buttons is a bit vague and we don't have an option to change the responded to after it's posted.

We are here to share knowledge for whomever is listening. If you already know, there's absolutely no need to criticize the source of valid information.

[ceyhunyuzuak]

Of course there is nothing wrong with sharing information but if you address that to particularly somebody, who tries and shares a valid answer to the main question, although he mentioned that he hadn't even slightly understood for what purpose that "answer" will be used, what you share immediately become something you use too boost up your tiny ego.. if that's the case, at that point I wouldn't try not to be condescending.

But maybe I should've waited and been sure before being arrogant, though. you may be right. I don't know.

[iainsavage]

I was responding to this below because for domestic hot water systems passing the supply flow into the return is factually incorrect. 

3. if you want to keep the flows in a coordination you should set one connector element as preset and the other one calculated based on which side defines the flow rate. for instance let's say your DHW system accumulates the end point needs and has already flow defined at the end. pick the connector element that has flow direction defined as "out" (assuming here your "out" side is DHW) and set its flow configuration "Calculated" and the other one as "Preset". bind both of their "Flow" to the same instance parameter you create. just create one and name it something.

[iainsavage]

This is nothing to do with ego.

Your advice in part 3 above was wrong and I was hoping to avoid errors in the OP’s model and for anyone else reading this post in the future.

I don’t see any need for you to resort to insults, that does not help the OP or anyone else to obtain the answer.

[ceyhunyuzuak]

yes. you should have already thought about the possibililty that I put that "number 3" just in order to inform people who will look at this topic in the future with a question in their head if keeping systems separated but analytically connected is possible.

back in the days I started to work with Revit, I needed to generate that method, which I still use pretty much in my every single project, and now I found a chance to share it. 

I don't think anyone will come here to learn how hot water storage tanks work, or how one can calculate high school thermodynamics. 

[iainsavage]

No good deed goes unpunished.

Have a good weekend.

[iainsavage]

…..and in another post earlier this month you said:

as an HVACR BIM Engineer I have pretty much never used plumbing discipline until several of days ago. 

recently as I didn't have much to do in terms of projects I wanted to go ahead and learn some plumbing.

I would classify domestic hot water as plumbing so apologies for assuming, based on your own words, that you might not understand the calculation methodology.

Anyway, hopefully my comments will be  of value to someone else in the future, maybe an undergraduate with less knowledge than us?

[ceyhunyuzuak]

1. that topic was about plumbing standards and their fixture units to flow conversion algorithms.

2. As you are presumably already aware, thermodynamic laws are universal, therefore it applies same way in plumbing and in air conditioning, also in combustion engines, in gas turbines, in living organism cells and so on...

3. in that very topic I revealed what my profession is. so I think I have right to expect you to know that I finished at least highschool.

I appreciate your good deeds, sir, indeed I do, although I find myself in a bit of a struggle in terms of finding any good deeds among your underlined capital bold "not"s.

But I want to humbly suggest you to take a deep breath be sure that what you are about to comment is actually relevant and needed or is it something you just want to rub against people's faces. 

if you still insist that it was all good intention, I'm ready to publicly apologise for misinterpreting your approach.

[iainsavage]

It was all good intention.

Have a good weekend.

[ceyhunyuzuak]

Please accept my apologies, sir.

Have a good one 🙂

[iainsavage]

Thank you.
Lets move on.